Leather treatment

ABSTRACT

Leather having improved resistance to shrinkage on exposure to high temperatures as occasioned by flash fires is produced by impregnating leather with a salt of a metal selected from the transition metals of the fourth and fifth periods of the Periodic Table and magnesium, such as nickel, chromium, cobalt, manganese and magnesium. Treatment of the impregnated leather with a linear addition polymer of trifluorovinyl chloride and treatment of impregnated or unimpregnated leather with microwaves results in an increase in the shrinkproof character of the leather.

United States Patent [1 1 Miller Nov. 27, 1973 1 LEATHER TREATMENT [75] Inventor: George T. Miller, Lewiston, N.Y.

[73] Assignee: Hooker Chemical Corporation,

Niagara Falls, N.Y.

[22] Filed: Aug. 16, 1971 [21] Appl. No.: 172,269

[56] References Cited UNITED STATES PATENTS 2,772,988 12/1956 Plapper et a1 117/142 X 2,326,233 8/1943 Leatherman 117/137 X 3,038,818 6/1962 Findlay 117/142 X 2,188,746 l/1940 .Bersworth.... 8/94.26 X 2,999,768 9/1961 Boresch 117/142 X 3,102,772 9/1963 Robinson 117/142 X 2,686,738 8/1954 Teeters 117/161 X 3,484,179 12/1969 Adams et al..... ll7/93.1 X 2,618,796 11/1952 Brophy l17/93.1 UX 3,419,344 12/1968 .lones.... 117/137 X 3,061,468 10/1962 Tryon 117/138 3,516,980 6/1970 Dore et al 117/142 X 3,268,360 8/1966 Beninate et a1 117/142 X 3,378,609 4/1968 Fasicket a1 1 17/136 X 3,463,665 8/1969 Quinn 2,865,790 12/1958 Baer ll7/93.1 FOREIGN PATENTS OR APPLICATIONS 180,758 6/1922 Great Britain 117/142 OTHER PUBLICATIONS Wilson, Modern Practice in Leather Manufacture, pp. 521-523 (1941).

Chakravorty et a1., Uncommon Inorganic Tannages, Jour. Soc. Leather Trades Chemist, Vol. XLI, 1958, pp. 2-10.

Primary ExaminerWilliam D. Martin Assistant Examiner-Harry J. Gwinnell Attorney-Peter F. Casella et a1.

[57] ABSTRACT Leather having improved resistance to shrinkage on exposure to high temperatures as occasioned by flash fires is produced by impregnating leather with a salt of a metal selected from the transition metals of the fourth and fifth periods of the Periodic Table and magnesium, such as nickel, chromium, cobalt, manganese and magnesium. Treatment of the impregnated leather with a linear addition polymer of trifluorovinyl chloride and treatment of impregnated or unimpregnated leather with microwaves results in an increase in the shrinkproof character of the leather.

10 Claims, No Drawings LEATHER TREATMENT This invention relates to methods for increasing the resistance of leather to shrinkage on exposure to heat. More particularly, the invention concerns the treatment, by impregnation, of leather with salts of certain metals whereby the leather has improved resistance to shrinkage on exposure to heat as by hot water or flash fires.

BACKGROUND OF THE INVENTION It is known that gloves, boots, jackets and other articles of apparel are often fabricated of leather and that such articles, especially gloves, tend to shrink excessively when exposed to high temperatures for relatively short periods, as in the case where they are exposed to a flash fire. The shrinkage may be so severe that the glove or other article must be cut off the wearer. The result is that serious burns and other injuries have occurred when the wearer has been exposed to a flash fire.

Many processes for the fireproofing and shrink proofing of leather have been suggested by those skilled in the leather art. For example, U.S. Pat. No. 3,419,344 discloses a two step treatment of conventionally mineral tanned leather whereby the leather is initially treated, retanned, with a phosphonium halide and then the 'retanned leather is subjected to a fat liquoring step with a phosphate ester. The initial retanning is said to impart resistance of the leather to afterglow while the second step aids in rendering the leather resistant to combustion. This procedure decreases high temperature shrinkage only slightly and does not significantly extend the use of the leather where high temperature dimensional stability is important. Other methods have not been wholly successful for the reasons that they impart undesirable effects on the hand of the leather or the degree of improvement in resistance to high temperature thermal shrinkage is too small to substantially effect the leathers utility. Further, it is known (see Doklady Akad, Navk. S.S.S.R 82 4058 1952) that conventional tanning processes do not significantly affect the high temperature (dry collagen) dimensional stability, although the hydrothemial dimensional stability of the tanned leather may be improved.

OBJECTS OF THE INVENTION It is, therefore, a principal object of this invention to provide leather having improved resistance to shrinkage on exposure to high temperatures while maintaining a useful hand and tactility.

Another object is to devise processes for treating leather which imparts thereto improved resistance to shrinkage on exposure to heat.

Other objects will be obvious from the following de-- scription of the invention.

BRIEF SUMMARY OF THE INVENTION These and other objects of the invention are accomplished by contacting leather, preferably after it has been tanned and fat liquored, and which may or may not be finished, with a solution of a salt of metal selected from the group consisting of the transition metals from the 4th and 5th period of the Periodic Table and magnesium.

The treatment bath is preferably warm, i.e., from about 40 to about C.

Sufficient of the metal salt solution is used so as to impregnate the leather with an amount of the salt which is at least about 0.5 percent by weight of the leather.

The treated leather thereafter may be dried in a moderate oven or by exposure to air.

The leather can be treated also with a linear addition polymer of trifluorovinyl chloride preferably after the impregnation of the leather with the metal salt.

Preferably the leather is exposed to microwaves, either before or after the impregnation with metal salt. Microwaves, i.e., high frequency radiation of about I00 megahertz to gigahertz can be used to treat the leather. This preferred treatment may be accomplished by subjecting the leather before or after impregnation and/or with the leather in a wet or dry condition.

In the description which follows, glove leather will be used in the specific embodiments. It should be distinctly understood that the principles of the invention apply with equal force to other leathers, that is to say that the broad principals of the invention encompass the shrinkproofing of leather irrespective of their intended use or classification. Thus, the invention applies to the treatment of the skins and hides of all animals including cattle, horses, sheep, goats, pigs and the like. It is preferred to treat the leather in the tanned state, especially chrome tanned leather, and preferably after fat liquoring. Although the leather can be treated before or after finishing, it is preferred to treat it before finishing. The leather can be treated before or after fabrication into a useful article. Thus, for example, fabricated gloves can be treated by our process, or the skin can be treated and then fabricated into a glove or other useful article.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, leather, preferably that which has been subjected to the customary mechanical operations which follow the tanning step, is immersed in asolution of a salt of a metal of the above defined group, and the leather is worked in the solution until it is thoroughly impregnated with the treating solution. The leather, after removal from the solution may be rinsed and dried.

Preferably the leather to be treated, is a metal salt tanned leather and especially that which has been fat liquored. At this stage in manufacture, the leather is referred to as in the crust. Although preferably treated in the crust," the leather may also be treated after subsequent finishing steps such as drying, lacquering, etc.

The metal salt solution is preferably an aqueous solution, although organic solvent solutions can be used. Solvents such as alcohol, acetone, trichloroethylene, benzene, n-hexane and the like can be used. The solvent should be one, or a mixture thereof, in which the metal salt is soluble to the extent of at least one percent by weight.

Sufficient of the solution of the metal salt should be used so that the impregnated leather after treatment will contain at least 0.5 percent metalsalt by weight.

The temperature of the treatment bath may be varied over a wide range, e.g., from about 5 C up to the boiling point of the bath. Preferably the treatment bath is at a temperaturewithin the range of about 40 to about 85 centigrade. At lower temperatures, the rate of impregnation may become impractically slow whereas at high temperatures, e.g., approaching the boiling temperature of the bath, the leather may undergo shrinkage before the shrinkproofing character of the invention has been imparted to the leather.

Conveniently, the treatment solution can be an aqueous solution of the metal salt of a concentration within the range of about 5 percent by weight and about forty percent by weight. Saturated solutions can be used although such are not necessary and hence not to be preferred.

The metal salts generally used contain one or more of the transition elements of the fourth or fifth period of the Periodic Table or the alkaline earth metal, magnesium. Thus, salts of nickel, cobalt, chromium, manganese, magnesium, copper and zinc are typical of the metal salts which can be used.

The metal salts found effective in this invention can contain a wide variety of anions. Suitable anions include the chlorides, bromides, sulfates, phosphates, carbonates, nitrates, oxyhalides, formates, acetates, propionates, oxalates, carbamates, tartrates, stearates, oleates, palminates and the like inorganic and organic anions as well as mixtures and hydrates thereof. Further, the metal salt can be complexed with complexing agents such as ammonia, quinoline, pyridine, various amines and the like. Further, various double salts may be used such as copper potassium tartrate, nickel potassium sulfate, magnesium sodium sulfate and the like.

This invention includes also the insitu reaction within the leather structure of various salts so as to produce substantially insoluble metal salts within the leather structure which treatment imparts resistance to thermal shrinkage. Thus, various metal salts can be precipitated within the leather structure by reaction with fatty acids, bases, oxidants and the like. Either the leather can be treated with the solution of a metal salt as previously described and then with a reactant to effect the formation of an insoluble metal salt or the leather can be treated with the precipitating reactant and then with the metal salts. Thus, for example, the leather can be treated with aqueous ammonia and subsequently with nickel sulfate, the leather can be treated with nickel sulfate and subsequently with ammonia to precipitate the metal salt or the nickel sulfate ammonia complex can be dissolved in excess aqueous ammonia, soaked into the leather and subsequently precipitated by removing the excess ammonia by evaporation, reaction with acidic constituants in the leather and the like.

The treatment vessel can be any vessel in which the leather can be placed in intimate contact with the solution. Open or closed vats preferably provided with means to gently agitate the leather during treatment are used. Rotating vessels, e.g., tanning drums, are convenient for this purpose.

The treated leather can be washed with cold to warm water or solvent after impregnation and before drying, if desired.

The time of the impregnation treatment can be varied considerably. The period of treatment should be adequate to permit reasonably thorough penetration of the metal salt solution. As will be evident to those skilled in the leather art, the porosity of leathers vary over a wide range depending on the type of leather and the pretreatment thereof. Under normal conditions, a chrome tanned cow hide leather can be impregnated in a warm, e.g., 50 to 60 centigrade, solution in a period of from about 10 minutes to one hour. Longer periods of time can be used, but such are usually without sufficient additional beneficial effect as to warrant the additional effort.

It has been found, and it is therefore an additional feature of this invention, that the shrinkproofing effect of the metal salts defined above, can be improved by the treatment of the leather with a linear addition polymer of trifluorovinyl chloride. Such polymers have the formula and are available commercially in various grades varying according to average molecular weight from about 500 to about 1,700. Preferably, polytrifluorovinyl chloride polymers of average molecular weight within the range of about 775 and 1,000 are used.

The polymer in amount of about 10 to 40 percent by weight of the leather, and preferably about 20 to 25 percent, is worked into the metal salt treated leather.

The polytrifluorovinyl chloride treatment has been found to provide a synergistic improvement in the shrinkproof character of the leather. This synergism is indicated by the following facts.

1. Leather treated with polytrifluorovinyl chloride on being exposed to a flame for about 7 seconds shrank about as much as an untreated leather.

2. Leather treated with an aqueous solution of nickel sulfate then dried and thereafter exposed to a flame for seven seconds shrank about fifteen percent of its original size.

3. Leather treated with nickel sulfate as in 2) above, then with a polytrifluorovinyl chloride polymer as in 1) above, and thereafter exposed to a flame for 7 seconds shrank only 6 percent of its original size.

Such a test is indicative of the synergistic effect of treating leather impregnated with a water soluble nickel salt and then with a trifluorovinyl chloride polymer.

It has been found, and it is a further part of this invention, that leather exposed, either in the wet or dry state, before or after treatment thereof with the salts of the invention, to microwaves, that is, radiation of high frequencies between the range of about megahertz and 100 gigahertz, also improves the resistance to shrinkage of leather exposed to high temperature, as well as to the temperature of boiling water. Further, microwave treatment of leather, in either the wet or dry stage, and without impregnation of the leather with metal salts, also results in the improvement of the resistance to shrinkage of the leather on exposure to flames and to boiling water temperatures.

The following examples will illustrate the present invention. Unless otherwise indicated, all parts and percentages are by weight and temperatures are given in degrees centigrade.

EXAMPLE 1 A series of tests were conducted to demonstrate the effectiveness of various salts as agents to improve the shrinkproof character of leather on exposure to high temperatures in the following manner.

Four strips, measuring 1 1% inches by 1 inch, of white finished chrome tanned glove leather and of natural finish chrome tanned leather were used in each of the tests. The leather strips were completely immersed for 20 minutes at 60 in a 30 percent aqueous solutionof the indicated salt.

Two strips from each group were rinsed lightly on both sides with distilled water after impregnation and were then permitted to dry in air at ambient temperature for about 16 hours.

Two impregnated strips from each group were immersed completely in distilled water for minutes, during which period the water was decanted from the immersed strips and replaced with fresh distilled water. The soaked" strips were then permitted to dry in air for about 16 hours at ambient temperature.

The impregnated strips were then exposed for seven seconds in a furnace heated, with globar resistance elements, to 750. After removal from the furnace the strips were measured. The average of the dimensions of the two similarly treated strips in each groups is set out in Table 1 below.

As a control, two 1 1% inch by 1 inch strips of each type of leather, which werenot treated in any fashion, were similarly exposed to heat.

seconds in a fumace heated with globar resistance units 7 and then measured.

The white finished leather samples measured 1 inches by 78 inch and natural finish tanned leather strips measured 1 /16 inches by "/a inch.

Untreated control strips after similar exposure to a temperature of 750 for 7 seconds had shrunk to 1 inch by 11/16 (white finished leather) and 1 inch by fiveeighths inch(natural finish leather).

EXAMPLE 3 TABLE 1 White finished chrome Natural linisll chrome tanned leather tanned leather Impregnating salt Rinsed Soaked Rinsed Soaked Remarks Control 1 x 1 x $4 M 2113 92 1 C080 1% x %6 L745 x M 1% x 1% x Strips curled. NiS04 /io iie im CrSOr 1 /ax A5 1%x 6 FMGXM; 1% x% F0804 1%H 1%x% 1%x M6 lyax m gs i 1 7 -Au 1946 X 1%X -io -"iia X /:i M11504. iio iia 011012. Shrunk Shrunk Shrunk I Shrunk NaGl. 1i x% lx% 1%ax% ax m All curled. Na2S04 1 4x 94 1%x% 1%x% 73X% 1J0.

1 Severely shrunk. 2 Shrunk and hard.

Notes:

a. All dimensions given in inches.

b. A strip of white finished chrome tanned leather impregnated with nickel sulfate and rinsed as described above was found to contain 3.35 percent c. The nickel sulfate impregnated soaked leather was found to contain 2.62 percent Ni.

d. The chromic sulfate impregnated rinsed leather was found to contain 4.15 percent Cr.

e. The chrome sulfate impregnated soaked leather contained 3.69 percent Cr. I

These results indicate the improvement in the resistance to shrinkage on exposure to high temperatures of leather impregnated with salts of chromium, nickel, magnesium, manganese and cobalt.

EXAMPLE 2 Four'strips, 1 1% inches by 1 inch, of white finished chrome tanned leather and of natural finish chrome tanned leather were immersed in 10 percent aqueous nickelous sulfate at 60 for minutes. The strips were washed by holding them under hot running tapwater for several minutes andthen dried on paper towels in air at ambient temperature for about 16 hours. The

, samples were exposed to a ternperature of 750 for 7 and held in an oven, one over the other, for 13 seconds at 700.

The treated glove shrunk 22 percent in volume and resisted ignition, although the finger tips smoldered. However, the palm of the untreated glove burst into flame, which was extinguished upon removal from the oven. The glove shrunk 48 percent in volume and was very stiff.

EXAMPLE 4 Five centimeter square pieces of chrome tanned sheepskin leather as used for Air Force gloves were immersed in 350 milliliters of 10 percent aqueous nickel sulfate at The leather squares were permitted to soak in the solution for twenty minutes with occasional stirring. The leather squares were then rinsed with distilled water for about 1 minute and then dried on a towel under ambient conditions for about 16 hours.

Various quantities of a commercially available linear addition polymer of trifluorovinyl polymer were worked into the treated leather squares. The treated leather squares were laid side by side and covered with aluminum foil having 8 holes of one-half diameter, one over each sample. The covered squares were then exposed to the sweep of the flame of a Fisher burner for about 15 seconds (temperature about l,200 C, the

flame being swept at a uniform rate over all the samples, impinging on the leather where exposed in the one-half inch diameter hole. The results from this series of tests are set out in Table 11 below.

These data indicate the surprising efficiency of the combination of a metal salt, e.g., nickel sulfate, and a linear addition polymer of trifluorovinyl chloride which when incorporated in leather in the manner of this in- TABLE II Weight of Weight; of sample Weight Loading. sample plus 01 grams/ Sample (grams) polymer polymer cm. Shrinkage Control 1.05 Ni only 1.22 Ni plus largo polymer.. 1. 25 2 1 O D0. Ni plus medium polym 1. 46 2.17 1 0.71 0.03 Nil. Ni plus small polymer. 1. 31 1. 61 1 0.30 0.01 Nil. Ni plus medium polymer. 1. 22 1. 73 Z 0.51 0. 02 Very slight.

1. 35 1. 99 3 0. 61 0. 03 Ni]. 1.47 1.58 1 0.11 0.004 Slight.

D Ni plus little polymer" Legend:

Little Polymer 1/16 of weight of leather used. Small Polymer A of weight of leather used. Medium Polymer 1% of weight of leather used. Large Polymer equal weight of leather used.

(1) Polymer of 965 average molecular weight. (2) Polymer of 560 average molecular weight. (3) Polymer of 1,550 average molecular weight.

EXAMPLE 5 Five chrome tanned leather strips, of equal dimensions, were treated as follows:

Strip 1) Immersed in percent aqueousnickel sulfate solution at 60 for minutes, rinsed with distilled water and dried in a 50 oven for about 16 hours then placed in a dessicator.

Strip 2) Impregnated with nickel sulfate as in strip 1, and a medium amount, 19 percent by weight of the leather strip, of a linear addition polymer of trifluorovinyl chloride, average molecular weight of 965, was worked into the leather strip.

Strip 3) Treated as Strip 2, except that only a small amount, 8.2 percent of the polymer, was worked into the leather.

Strip 4) Treated only with a medium amount, 20.4 3 percent of polymer.

Strip 5) Control strip, no treatment.

All five strips were covered with aluminum foil having one hole of one-half inch diameter located over each sample. The covered strips were exposed to the flame of a Fisher burner for about 15 seconds as in Ex- 4 ample 4. The thickness of the center of the exposed areas and the original thickness as measured at the unshrunk edge of the sample was determined by micrometer after the exposure to the flame to determine the extent of the shrinkage caused by the heat treatment. Several measurements were made and the average dimension calculated. That the linear shrinkage could be computed from thickness increase was previously verified.

The data computed in thrs series of tests is shown in TABLE 111 below:

vention, increases the resistance to shrinking of the leather when exposed to high temperature. Moreover the combination of the metal salt and polymer result in a synergistic improvement, for the polymer, per se, has been shown to provide little or no shrink proofing, while the combination of the metal salt and polymer provide substantially greater protection than the metal salt alone.

EXAMPLE 6 a. This experiment'demonstrates the beneficial effect of microwaves on leather. In this and other experiments in this series, a Heath Microwave oven operating at approximately 2,450 megahertz was used.

Three pieces of chrome tanned sheepskin glove leather were treated as follows:

One piece was impregnated with nickel sulfate by immersing the leather piece in warm (60 to 10 percent aqueous nickel sulfate for 20 minutes, rinsing with distilled water for about 1 minute, and drying.

A second piece was impregnated with nickel sulfate as above and then heated in the microwave oven for four minutes.

A third piece was untreated and used as a control.

A strip 70 mm long-by 8 mm wide was cut from each of the above samples at right angle to the direction of hair, as determined by examining the follicles.

The three strips then were placed in 200 milliliters of distilled water and heated therein at the boiling temper- 5 ature for ten minutes. The strips were removed and examined.

The control and nickel impregnated (but not exposed to microwaves) strips were tightly curled whereas the strip which was exposed to microwaves was essentially straight.

The control strip, after contract with boiling water, had shrunk to 35 mm length, a 50 percent shrinkage.

The nickel impregnated strip had shrunk to 40 mm length, a 43 percent shrinkage.

The microwave treated strip had shrunk to 46 mm length, a shrinkage of only 34 percent.

b. This series of experiments show the beneficial effect of microwaves on leather with respect to the improvement of the resistance of the leather to flame temperatures.

In these tests a pinch clamp, tied to a suitable support, was used to fasten the leather strips. At a point 40 mm from the pinch clamp, an alligator clamp was fastened t0 the strip, and the clamp was fastened by wire to nylon thread to which a 148 gram weight was attached, the nylon thread passing over a horizontal bar. A separate weighted alligator clamp was used for each leather strip so that the leather could shrink independently under the same constant tension and the same 40 mm length of leather could be exposed to the flame in each instance. A Fisher. burner, having a 3.5 cm top, was placed at a distance of 4 cm below each of the test strips. Thus the leather strips were positioned side by side, each under the same tension, and heated simultaneously by the flame.

Three strips were tested, one an untreated control, one impregnated with nickel sulfate, as in part A above, and a third strip impregnated with nickel sulfate and then heated while wet (i.e., the strip had not been dried after impregnation) in the microwave oven for 4 min utes.

The strips were exposed to the flame for a 5 second period. Immediately after removal of the flame, the strips were blown on to extinguish any flaming and to stabilize the leather.

The original 40 mm section of the control strip had shrunk to 30 mm, a 25 percent shrinkage.

The nickel impregnated strip had shrunk to 33 mm, a 17.6 percent shrinkage.

The microwave treated strip had shrunk to 34 mm, a 15 percent shrinkage.

The results of these tests prove that leather on exposure to radiation of microwave frequency is beneficially altered with respect to its resistance to shrinkage on exposure to high temperatures within the range of about 100 (boiling water) and about 1,200 (flame temperature).

EXAMPLE 7 This example illustrates the effect on hydrolytic stability of chrome tanned sheepskin leather treated in accordance with the invention with metal salts and micro- TABLE IV Sample Final Length Shrinkage Control 35 mm 50 NiSO treated mm 43 M80. treated Microwaves 46 mm 34 These data indicate the pronounced improvement in the resistance to hydrothermal shrinkage effected by the combination of metal salt impregnation and exposure to microwaves of leather in accordance with this invention. I

EXAMPLE 8 Samples measuring 1 2% inches X 54 inches were cut from untreated chrome tanned sheepskin and the same leather treated with 10 percent Niso at 60 for 30 minutes, rinsed, and dried. Samples were cut parallel and at right angle to the hair direction. The smaples were clamped in an Inston testing machine, placed under an initial tensile load of 0.04 lb (18 grams) and the stress vs. time measured as the samples were flamed with a wing tip propane torch.

The control samples showed an initial rapid increase in stress for about the first 0.01 minutes, a continuing increase but at a slower rate for the next 0.03 minutes and a second rapid increase in stress for the next 0.04 minutes, approximately, at which time the leather underwent flow as it burned and the stress decreased steadily to failure.

The treated samples showed the same initial increase in stress, but remained at that stress value without undergoing the continuing increase in stress noted with the control samples.

The stress values at 0.02 and 0.04 minutes were as follows:

Untreated Treated Sample Cut: Min. Leather Leather Stress Stress Parallel to hair 0.02 0.56 lb. 0.54lb direction at 0.04 1.04 lb. 0.54 lb Right Angle to 0.02 0.36 lb. 0.17 lb hair direction 0.04 0.63 lb. 0.22 lb These data demonstrates that the leather shrinks by a two stage process. They further demonstrate that the treatment in accordance with the invention is particularly effective in controlling the second stage of shrinkage at higher temperatures whereas conventional tanning processes have negligible effect.

EXAMPLE 9 Gray Cabretta (chrome tanned sheepskin) was treated as follows:

Sample Nl was treated with 10 percent aqueous NiCl '6l-l O at 60 for 12 minutes.

Sample NN was treated with 10 percent aqueous NiCl -6H O to which was added ammonium hydroxide in amount sufficient to dissolve the initial precipitate. The treatment was for 12 minutes at 60.

Sample Nl-l Nl was first soaked in 6 percent aqueous Nl-LOH for 20 minutes at room temperature and then for 12 minutes at 60 in 10 percent aqueous NiCl -6H O.

All samples were rinsed in distilled water and dried in a forced draft oven at 53 for 18 hours.

The samples were tested by exposure of 3 mm wide strips, 30 mm long under 25 gram tension to a l,200 flame for 2 seconds. All samples were cut at right angles to backbone.

Shrinkage Control 40% Nl 30% N+N l 7% NH:,Nl 23% EXAMPLE l0 Deerskin gloves were treated as follows:

C Control Chrome tanned deerskin gloves C MW Exposed 10 minutes in microwave oven N F Treated with 10 percent aqueous NiSO at 60 for 20 minutes, rinsed, dried, 20 percent Fluorolube LG- worked into glove.

A N Soaked in 6 percent aqueous NH OH at ambient temperature for 20 minutes then in 10 percent aqueous NiSO at 60 for 20 minutes, rinsed and dried.

Mg Soaked in 10 percent aqueous MgSQ, at 60 for 20 minutes, rinsed and dried.

* Fluorolube LG-160 is a commercially available polytrifluorovinyl chloride polymer having an average molecular weight of 965.

The gloves were stuffed with glass wool and suspended in a kerosene fire for 3 seconds. The fire completely enveloped the glove. The shrinkage occasioned by this test was determined as the ratio of the volume of the glove before and after exposure to fire. Values indicated below are averages of 2 gloves for each treatment.

C 33.6% volume shrinkage C+MW 22.8% volume shrinkage N+F 0.4% volume shrinkage A+N 3.9% increase in volume Mg 4.6% shrinkage EXAMPLE 1 l The excellent resistance to shrinkage on exposure to flames of leather treated in accordance with this invention was further demonstrated by the following test.

Samples of leather from the leather gloves used in Example were attached to a steel ring by clamps and weighted by a 10 gram clamp. The samples were 3 mm by mm (marked length). All samples were held in the kerosene flame for the same time, three seconds. Linear shrinkage measured.

Sample Linear Shrinkage C C+MW 0.5 percent by weight of an ionizable salt of nickel, cobalt, chromium, manganese, copper, zinc, iron, or magnesium.

2. Leather as described in claim 1 in which the polymer has an average molecular weight of from about 500 to about 1,600.

3. Leather as described in claim 1 in which the metal salt used is a salt of nickel.

4. Leather as described in claim 1 in which the metal salt used is a salt of magnesium.

5. The process which comprises the steps of immersing a chrome tanned leather in an aqueous solution of an ionizable salt of a transition metal of the fourth and fifth periods of the Periodic Table or magnesium for a time sufficient to impregnate the leather with at least about 0.5 percent by weight of said metal salt, impregnating the metal salt containing leather also with a linear addition polymer of trifluorovinyl chloride, and drying the resultant impregnated leather.

6. The process as described in claim 5 in which the linear addition polymer has an average molecular weight of from about 500 to about 1,600.

7. The process as described in claim 5 in which the metal salt used is a salt of nickel.

8. The process as described in claim 5 in which the metal salt used is a salt of magnesium.

9. Chrome tanned leather having improved resistance to shrinkage on exposure to heat said leather having been exposed to microwave radiation and impregnated with at least about 0.5 percent by weight of an ionizable salt of a transition metal of the fourth and fifth periods of the Periodic Table or magnesium and impregnated also with a linear addition polymer of trifluorovinyl chloride.

10. Leather as described in claim 9 in which the polymer has an average molecular weight of from about 500 to about 1,600. 

2. Leather as described in claim 1 in which the polymer has an average molecular weight of from about 500 to about 1,600.
 3. Leather as described in claim 1 in which the metal salt used is a salt of nickel.
 4. Leather as described in claim 1 in which the metal salt used is a salt of magnesium.
 5. The process which comprises the steps of immersing a chrome tanned leather in an aqueous solution of an ionizable salt of a transition metal of the fourth and fifth periods of the Periodic Table or magnesium for a time sufficient to impregnate the leather with at least about 0.5 percent by weight of said metal salt, impregnating the metal salt containing leather also with a linear addition polymer of trifluorovinyl chloride, and drying the resultant impregnated leather.
 6. The process as described in claim 5 in which the linear addition polymer has an average molecular weight of from about 500 to about 1,600.
 7. The process as described in claim 5 in which the metal salt used is a salt of nickel.
 8. The process as described in claim 5 in which the metal salt used is a salt of magnesium.
 9. Chrome tanned leather having improved resistance to shrinkage on exposure to heat said leather having been exposed to microwave radiation and impregnated with at least about 0.5 percent by weight of an ionizable salt of a transition metal of the fourth and fifth periods of the Periodic Table or magnesium and impregnated also with a linear addition polymer of trifluorovinyl chloride.
 10. Leather as described in claim 9 in which the polymer has an average molecular weight of from about 500 to about 1,600. 